Introduction

There's been some talk of emergency Prius-starting when the 12V battery poops out. Here is something that looks like it could be a pretty good solution, along with a good deal on it. It's a compact, lightweight NiCd 12-V battery pack that ought to be plenty to "boot" a Prius. You can also plug 12-V Lighter-based accessories into it to run them externally. I'm thinking this would be good to carry around in the trunk or under the seat as an emergency cell-phone or computer supply. And in a pinch you'd have it to boot the Prius.

I just saw this at my local Radio Shack. It's on sale from $40 to $20 during May, 2003. Here is the RS link:

Coleman 2-in-1 Emergency Car Starter & DC Power Source

It's got 11 Sub-C sized NiCd cells at 1300 mAH. Yeah, NiCd isn't the best technology but when the NiCd's poop out, you can replace them with NiMH's for extended operation (at the expense of a little weight increase). Electrically, they should charge just fine in it. Here is a link to a page with a wide selection of replacement Sub-C sized cells. The high-end NiMH cells are 3000 mAH, more than twice the capacity of the original Coleman unit and would equal the capacity of a small laptop battery.

OnlyBatteries.com Sub-C NiMH and NiCd

I don't work for Radio Shack or Coleman (or OnlyBatteries.com) and I have no financial interest in those companies or in this item. Nor do I make any claims for fitness for any potential purpose. ;^> I'm just passing it along as a heads-up.

Pictures

Here are some pictures of the unit, including one opened to show the battery pack.

Coleman Powermate Car Starter.

Coleman Powermate Car Starter, opened.

Using it as a Prius Emergency Starter

From reports of other car starters, we've discovered a caveat in using it as a Prius emergency starter. The typical case when you'd need this is when you have a completely dead 12-V battery. This is not hard to get in the Prius, since the battery drain of about 75mA just sitting in the driveway will deplete the battery in about 2 weeks.

The 12-V battery in the Prius is used to start up the computers which start the power inverter and use quite a bit of current to start the brake power-assist pump (15-20 A for a limited time), according to reports on the Yahoo Prius Technical Stuff discussion list. If there isn't enough juice to start up the initial inverter to get the 274-V batteries online, there won't be enough juice to close the ignition relays which patch the Accessory (cigarette-lighter) outlet to the battery line. This ignition relay prevents you from just plugging the Coleman unit into the Prius Accessory outlet to start the car on a dead 12-V battery.

You can see the relay in this page from the Prius wiring manual. It is the second relay from the top on the left side (labelled "ACC Relay"). You can see the Accessory-socket fuse on the right (labelled "15A CIG") coming out from the relay. The relay requires battery power through the ignition switch before it will close and connect the Accessory socket to the battery circuit.

There are two solutions to this problem.

1. Add a new Accessory (cigarette-lighter-type) outlet right on the battery circuit. This can be done at the fuse panel, or more safely right at the battery in the trunk. Use heavy cable to accommodate the 15-20A brake power assist pump current. 16-18ga should be fine.
   
2. Add a modification to the wiring or the fuse panel to patch the Prius Accessory outlet right to the battery circuit. Coastal Electronic Technologies offers a kit to do this. There has been caution voiced on the Prius Technical Stuff discussion list about the current surges in starting and the ability of the Accessory socket wiring to handle this. If you rewire your Accessory socket or add a new one at the fuse panel and use a boost battery like the Coleman Car Starter, you do so at your own risk.

If you are a member of the Prius Technical Stuff discussion list, you can go to this folder in the files section to see a number of other 12-V battery issues including general info, alternatives, and boost solutions.

Copyright © 2003 John R. Haggis. All Rights Reserved.
Last updated: 5/22/2003